1988 F250 351 remanufactured just installed

I'm still having this annoying condition Any ideas please?

At cold start up and without hitting the accelerator the truck will run 5 seconds then die. This will happen 2 or 3 times before it will continue running at about 1100 RPM for 15 seconds and then fall off to 700 RPM or so. The truck idles but shutters and rocks as if missing. This will go on until I take off.

Also, after the fall off to 700 RPM, if I rev the engine up to 1500 RPM a noticeable pulsing type miss will be felt. In other words opening the throttle and adding more air does not seem to remedy the situation.

I have a new distributor, module, rotor, cap, wires, and plugs. The injectors were refurbished. The tank, both fuel pumps and filter are new.

I replaced the TPS, ECT, and EGR sensors. I replaced the IAC ($72.00) this morning and still no change.

My codes reading say system pass #11.

I did replace the fuel pressure regulator during the new engine installation with a Bosch after market that looked almost new from the boneyard (out of an 1988 F250 351).

The truck runs great on the highway, lots of power and no noticeable irregularities.

If that regulator was bad wouldn't it show up at all speeds?

F.Y.I. Before I replaced the engine I also had wacky cold start issues. Sometime it would not have increased idle and die several times during warm-up. Other times after going down the road a mile or so and coming to a stop the truck would be racing at 2000 RPM. I had always found that turning off the key and restarting would eliminate the high RPM. Like re-booting a computer. Hope this helps with ideas!

 

Jemini,

Try replacing the EEC IV with one that is good from a junkyard....just a thought as it seems you have tried everything else.

Johnny


1988 Ford F-150 Custom 4.9L EFI 4 speed glass pack dual exhaust ally wheels
1990 Ford Mustang LX 5.0 Hatchback AOD Bassani X pipe with Flowmasters
1993 Ford Mustang LX Coupe 5-speed


................................God Bless Bless Henry Ford....................................

 

Thanks. I had that thought too. Hard to think the truck would run so great on the highway and so lousy at idle if the EEC IV was crappy. But old computers do wierd things even new ones act strange. That might be the problem.

 

buddy of mine recently had this problem, had to do with sensor,switch that controls Idle for ac on off, if you have this setup maybe something to ck. buddys out town, not sure name of part. hope this helps.

 

I just ran a KOER test and pulled a 41 - HEGO senso circuit indicates system lean or switching not detected.

The KOEO test still show 11 - system pass.

I just replaced the O2 sensor during the install. Hard to believe the sensor is bad.

May be the fuel at idle is not smooth and steady giving it that rough condition.

What should I see with a fuel pressure test? Should the pressure be up with the key on and the pumps having primed the system? What is an idle reading? What should the reading be with the engine at idle?

 

On the 41, if you run the KOER before the engine is fully warmed, you're liable to see several different codes that really don't mean anything yet. If you're sure the engine was at operating temp, then it's possible the HEGO wires got pinched, or there's just a bad connection somewhere.

Now as far as fuel pressure goes, if you run the fuel pump test from the DLC, with the engine off, you should see 45-50 PSI at the rail. Crank the truck, and you should see 35-40 PSI at idle. The Fuel Pressure regulator works on vacuum. More vacuum (closed throttle) less pressure. Less vacuum (WOT) more pressure. I used a handy-dandy hand-held vacuum pump to operate the FPR using the DLC connections with the truck cold to avoid flash fire caused by any leakage vaporizing, and possible ignition by a stray spark from a wire.

 

replace the Idle control motor .

Then set curb idle .

Crank her up , unplug the idle control motor , and turn the set screw in the throttle body until it idles at 700 . Plug back in motor . Done .

 

Ok, many people assume that little screw is for adjusting idle. It is NOT for adjusting idle. It is merely a stop screw which is set to keep the throttle plates from binding in the body. The plates should be FULLY closed with the throttle fully released, but should not bind or stick in the closed position. The IAC and the little holes in the throttle plates are for idle control, as well as vacuum regulation. The EEC senses RPM, MAP (Manifold Air Pressure), engine coolant temperature, and air charge temperature to decide what to do with the IAC. You said you replaced the IAC, but you wouldn't be the first to get one off a shelf that hangs up. Your problem may not be too much air through the IAC, but perhaps an EGR leak (burnt seat, sticky valve, etc) or maybe the plenum gasket got hosed up putting it on. Dunno, but your miss/stalling problem seems like a lean miss condition. Vacuum leaks, etc, can do that. I assume you have a Speed Density setup on your 88. I don't think Mass Air systems started showing up until '94 or so. Any vacuum leak anywhere on that system will cause a fast idle, especially when cold and there's plenty fuel to burn. This typically results in the cylinder closest to the leak to run lean, and miss. Other things to check for vacuum leak is the canister purge solenoid. Those too go bad, and will suck air in through the canister. That air may have some fumes from the tank, but not enough to keep the engine running properly. Go buy a pack of rubber caps, and disconnect EVERYTHING from the plenum except the MAP sensor. Yes, the brake booster too. Your problem is at idle, so you don't need power brakes at the moment. Something to remember is that at idle, you have the highest vacuum on the intake. With everything except the MAP capped off, start the truck and put a vacuum gage on one of the nipples. If you don't have at least 18 inches vacuum at idle, you got a leak somewhere. Use an unlit propane torch, and direct the gas all around the intake, EGR valve and all the vacuum fittings on the plenum. If there's a leak you'll hear the miss smooth out when it pulls the propane in. (again, assuming your ignition's in tip-top order). If you don't find anything, reconnect the vacuum lines one at a time until your problem rears it's ugly head again. Start with the brake booster. Sometimes the diaphragm in the booster will fail. This is usually accompanied by a sucking noise inside the cab, or funky braking. Not bad braking, just an occasional hard pedal. You can also take a tin can (NOT ALUMINUM!!) and cut a plate to put between the EGR and the plenum. That will tell you if the EGR isn't closing well. It won't hurt to run the truck with the EGR blocked, but you may see some reduced mileage and slightly higher engine temps. If the radiator/cooling system is good-to-go, you may not even see the temperature increase. The radiators in these trucks are huge compared to car radiators, yet it's the same engine. I know for a fact my t-stat will close on occasion in warm weather. After eliminating the booster and the EGR, move on to each line. Chances are, you'll find one that's split from dry rot or maybe got pinched a little during the engine install.

Despite your new wires, try this little FREE test. Park your truck in a dark place, start the engine, and look under the hood. If you see ANY spark whatsoever, you got a leaky wire. If ALL the fire doesn't make it to the plug with a .054 gap, it ain't gonna fire so good. I also assume you used good Motorcraft plugs (I forget the number). Trust me, Ford TFI's are VERY unforgiving about the spark plugs. They will EAT Bosch plugs, especially the Platinum II's or Platinum IV's. If a plug goes, it may actually cause a wire to fail too. If it can't spark, that's about 60,000 volts that wants to go somewhere. Unfortunately, it's normally out the side of a wire somewhere. I learned this the HARD way. Some swear by Motorcraft caps and rotors. That sort of depends on where you live, and how you drive the truck. Down south, with the humidity, I find copper electrodes in the cap hold up much longer than the aluminum ones. So, I'm running an MSD Cap/Rotor, but real Motorcraft wires and plugs. That made a LOT of my misfire go away. I don't run copper cap/rotor because it's a better conductor, I run them because they're more resistant to corrosion. We're only talking a few milliamps in the spark. Then again, my truck had 130,000 on it before I replaced the OE cap/rotor. I know, I'm the OO on the truck.

I chased rough idle problems on mine for a long time and spent a buttload of money before I found the bad plenum gasket. Yours is new, but are you sure it wasn't damaged on the install? Your ignition parts are new, but are they Motorcraft parts (especially the wires/plugs)? Lotsa places to look for a stumbling idle. Mine ain't perfect yet, but it runs a LOT better now than it did after 3 stealerships tried to fix it. They couldn't find the keyboard, gamepad or mouse port, so the 17 year olds in the garage didn't know what to do to it. Sometimes, it CAN be mechanical.

 

Old Paint,

Thanks for the information. I'm interested in that plenum gasket leak idea. How did you finally find that? I put my new plenum gasket on dry without sealant. I used two removeable studs to hold the gasket steady while I alligned the plenum and attached the bolts. It went on easy and I don't think it moved at all.

I tried plugging all the ports from the plenum except the MAP. Vacuum seem to be at 15 or 16, it never seems to get to 18. I put propane everwhere many times with no results. I especially shot the stuff all around the plenum gasket contact area. I didn't notice any change. Took the truck to a trusted mechanic who likewise shot carb cleaner everywhere with similar results. After he applied vacuum to the EGR without stalling of the engine, he thought the EGR was leaking. I replaced that unit with no change. Too much money outlay with no gain. I took the IAC back and I am thinking of returning the EGR. Thank-you Advance Auto for your great return policy! I had also returned the high pressure pump after determining that the check valve was leaking letting the fuel drain back into the tank. The old pump holds the fuel and pumps 39 PSI at the rail with one key turn.

I tried looking in the dark for spark leaks. I saw nothing except for a faint glow around the sides of the coil but no jumping leaks. I replaced the coil with at TFI stock replacement coil from MSD. My truck ran like crap and missed like crazy. I put back the old coil and it ran fine. Turns out I was only getting 3.8K on the secondary when the MSD should have been giving off 5.5K. Tech help at MSD said I had a bad coil. My wires are 8mm Belden and the plugs are Motorcraft. Cap and rotor were OEM with copper contacts.

I'm going to let another mechanic who is very familiar with EFI trucks test the system with a breakout box . He feels sure he'll find the culprit. I hope so cause I'm at a loss as to what to do next.

 

16 is too low. It's getting air from somewhere. You did unplug and cap off the little hose from the canister vent, right? It's at the front of the throttle body, just in front of the flange where it bolts to the plenum, but behind the throttle plates. Unless the throttle plates are stuck too far open, I can't figure out where the vac leak is at this point without a little hands-on time. If the plates are open, but the TPS has correct voltage, it'll idle too fast because the IAC will be closed, but still can't cut back the air. This usually causes lean miss at idle.

Sounds like you may need to run a compression test. Disconnect the low voltage connection on the coil. Remove every spark plug. Crank the engine with a gauge in one plug hole and record the pressure. Your readings may vary some, but acceptable readings are +/- 15% of each other.

Next question, was the vacuum pulsing? If it's pulsing, that's very bad news. That would indicate a stuck or burnt intake valve. If you didn't find anything external with the propane or starting fluid, with ALL the hoses except the MAP disconnected, chances are the plenum gasket is just fine. Dry is OK, but I prefer Permatex HYTAK on that one. Wonderful stuff on intakes.

Belden makes great wire for control systems and industrial applications. Motorcraft wires seem to be the only thing that will work reliably on Ford engines. I had a very expensive set of MSD performance wires that failed in less than 5000 miles. Looked like a Christmas tree under the hood. Glowing at the coil can't be good. I had a coil fail through the side, and arc to the laminated core of the coil. That was fun to find, and when it finally died, it killed the truck DEAD. Is your TFI module mounted on the dizzy, or on the fender well? I think 92 was the year they moved it to the fender because of a service advisory about TFI's heating up on the dizzy, and just shutting off. By the time the vehicle was towed to a stealership, it would crank up and run fine. Get it back on the highway, and bingo, dead motor again.

One more thing. The firing order on your engine should be 15426378. When you route your plug wires from the dizzy to the plugs, make sure that if two cylinders on the same side fire back to back, ESPECIALLY 7 and 8, that you keep the other wires from that side between those two as long as possible. This is the reason the firing order changed on the 5.0 in 94, as well as allowing the same cam to be used in two different engines (5.0 and 5.8). If 7 and 8 are side by side, you will get cross firing between those two. It will miss, cough, sputter, ping and drive you crazy. It will do this even with good Motorcraft wires on it. I learned this in the school of hard knocks. (excuse the pun)

 

Thanks Old Paint for the great info,

I passed on your insights to the mechanic who will run the breakout box test on Friday.

You know the truck runs like a champ on the highway. Would a sticky valve be noticeable only at idle or would it also affect crusing speed?

Also this is a remanufactured engine. This sucker should be top notch. I can't even deal with the idea of reinstalling another 351 even if it is on warranty with them paying me or someone $57.50 per hour to do it. I kept the crate sticker that said the engine was tested at 200 RPM (obviously not a true dyno test) and the cylinders were all reading 170 PSI. I haven't driven the truck 300 miles yet!

I'm going to take another look at plugging the hose from the canister vent. Boy if that is all it is!

About pulsing. The exhaust mechanic who is putting on the flowmaster cat back system called the idle condition by that name when he was checking out my truck. He said I better get that pulsing fixed or I could burn out the cat.

The TFI module is on the distributor and both are new.

I was really **** about the wire routing but I'll recheck that 5 & 6 go between 7 & 8 for as far as possible.

 

The innards of that cat are ceramic. Same stuff they put on the space shuttle's bottom. You'll melt the steel container before you hurt the innards.

Ok, TFI on the dizzy, but doesn't sound like an ignition problem. To prove this, get a spark plug boot puller, and see if one cylinder seems to be the culprit, or if it moves around. Pull a plug wire off one at a time, and see if the miss changes. If it doesn't, you just found the dead cylinder. Listen close to see if you hear any tapping noises. Possibly a pumped up lifter. It happens, but not often.

When I said pulsing, I didn't mean a sound. See if the vacuum gauge wiggles when attached to the plenum. It should be fairly steady. If there's a stuck/burnt valve, it'll bounce pretty badly. If you use the technique above to identify the dead cylinder, run a compression test again, especially on that cylinder. Run a leak-down test as well and check to see if the cylinder holds compression. I've seen some pictures somewhere of a home-made rig for leak-down test. I think the person used a gutted spark plug and a bicycle pump with a gauge.

I realize you have a new engine, but bad things happen to new things too. Don't wanna rain on your parade, just trying to give suggestions on what to look for. I'm certainly hoping you don't find any problems with the really bad stuff.

 

wow ..... then the book I have right here in my lap from Ford Fuel Injection class must have one helluva typo . States here precisely how to adjust Curb Idle ... like I said above .

But you should only adjust this AFTER you have fixed all vacuum line leaks .... new IAC , and it still refuses to idle right .

And like you said .... ne really needs to get a vacuum guage on there . I've had engines that have the lash too tight causing the valve to stay open a tiny bit , and had to shim the rockers . Vacuum test will reveal this .

 

your grandmas little figurines might be ceramic .... but a Cat converter is made of Platinum and Rhoadium I believe .

 

Just had a Flowmaster cat back installed (Delta Force 50 - 3" in and out).
Wow! Amazing power and smooth even at low RPM.

Flowmaster suggests a heat shield above the muffler. My stock shield was gone. The exhaust shop said I shouldn't need the shield as the exhaust will run somewhat cooler. Any ideas on this logic?

I re-routed the 7/8 wires to not run side by side in the wire separator.

A mechanic friend will do the full beakout box test this morning to try to run down the irratic idle problem.

My fingers are crossed!